When looking for synonyms for the phrase "cradle modern America," various options come to mind, including "birthplace of modern America," "nurturing ground for modern America," "genesis of modern America," and "starting point of modern America." These phrases all suggest the idea that modern America was born out of a particular place or time, and that it was nurtured or developed in that space. They also hint at the notion that modern America did not simply spring up spontaneously, but rather was the result of intentional processes and actions that took place over time. Overall, these synonyms help to convey the importance of understanding the historical and cultural roots of modern life in America.